This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to 99-48590 filed in Korea on Nov. 4. 1999; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to green-emitting phosphors for a plasma display panel (PDP) and a preparing method thereof, and more particularly, to green-emitting phosphors having excellent color purity and luminance characteristics so as to be capable of enhancing white color temperature and color reproducibility characteristics of a PDP, and a preparing method thereof.
2. Description of the Related Art
A general PDP forms a picture image using the luminance of a plasma discharge, or phosphors excited by a discharge, and operates by the following principle. That is, a predetermined voltage is applied to two electrodes installed in a discharge space of the PDP to cause a plasma discharge therebetween, and a phosphor layer having a predetermined pattern is excited by ultraviolet rays from the a plasma discharge, causing glow discharge, thereby forming a picture image.
Among materials for forming the phosphor layer, zinc silicate phosphors having excellent luminance characteristics are mainly used as green-emitting phosphors. Examples of the zinc silicate phosphors include Zn2SiO4:Mn, that is, manganese activated zinc orthosilicate, which, while poor in view of color purity, has excellent luminance characteristics.
With developments in the architecture and manufacturing process of a PDP, it has become a critical issue to improve the luminance of the PDP and to increase a white color temperature by improving the color purity of the PDP. Thus, a method was conventionally proposed in which a mixture of Zn2SiO4:Mn phosphor having excellent luminance but poor color purity and a barium aluminate phosphor having low luminance but excellent color purity was used.
However, even if the mixture of a zinc silicate phosphor and a barium aluminate phosphor is used, satisfactory color purity and luminance characteristics cannot be attained and there is still much room for improvement.
To solve the above problems, it is an object of the present invention to provide a green-emitting phosphor for a plasma display panel having excellent color purity and luminance characteristics, by which the white color temperature of the plasma display panel can be increased and color reproducibility can be enhanced.
It is another object of the present invention to provide a method of preparing the green-emitting phosphor for a plasma display panel.
Accordingly, to achieve the first object, there is provided a green-emitting phosphor for a plasma display panel, represented by the formula 1:
Ba1xe2x88x92xMnxAl12xe2x88x92yByO19xe2x80x83xe2x80x83[Formula 1]
wherein 0.001xe2x89xa6xxe2x89xa60.5 and 0.01xe2x89xa6yxe2x89xa61.0.
To achieve the second object, there is provided a method for preparing a green-emitting phosphor for a plasma display panel, represented by the formula 1:
Ba1xe2x88x92xMnxAl12xe2x88x92yByO19xe2x80x83xe2x80x83[Formula 1]
wherein 0.001xe2x89xa6xxe2x89xa60.5 and 0.01xe2x89xa6y1.0, the method comprising the steps of primarily firing a mixture of barium (Ba), manganese (Mn), aluminum (Al)and boron (B) compounds at 1000 to 1500xc2x0 C. in the presence of air, and secondarily firing the resultant material at 1000 to 1500xc2x0 C. under a reducing gas atmosphere.
Green-emitting phosphors for a plasma display panel are mostly caused to glow by incident UV light, that is, radiation with a wavelength of about 147 nm, and luminescence occurs only at the surface of a phosphor. Thus, the luminosity efficiency of a phosphor is considerably dependent on the presence of defects on the surface.
The present invention provides a green-emitting phosphor having a structure represented by the formula (1) by adding a boron (B) compound to a barium aluminate phosphor BaAl12O19:Mn illuminated by excited light, that is, radiation with a wavelength of about 147 nm, the green-emitting phosphor having excellent luminance and color purity characteristics. Here, the boron compound increases the absorption ratio of the excited light by increasing an energy band gap of the BaAl12O19:Mn phosphor having excellent color purity and improving the crystallinity of the phosphor. Also, the boron compound functions as a flux to reduce the defect of the surface of the phosphor, thereby improving the luminosity efficiency of the phosphor.
Ba1xe2x88x92xMnxAl12xe2x88x92yByO19xe2x80x83xe2x80x83[Formula (1)]
wherein 0.001xe2x89xa6xxe2x89xa60.5 and 0.01xe2x89xa6yxe2x89xa61.0.
In the green-emitting phosphor represented by the formula (1), x is preferably in the range from 0.03 to 0.3. More preferably, when x is 0.1, y is in the range from 0.2 to 0.4. In particular, when x is 0.1, y is preferably 0.2 to exhibit excellent luminance and color purity characteristics.
The green-emitting phosphor represented by the formula (1) according to the present invention is prepared by a solid-phase method, which will now be described.
First, as starting materials, a Ba compound, an Mn compound, an Al compound and a B compound are. mixed. Here, the mixture ratio by mol of these four compounds is 0.5 to 0.999 mol of Ba compound, 0.001 to 0.5 mole of Mn compound, 11 to 11.99 mol of Al compound and 0.01 to 1.0 mol of B compound. Examples of the Ba compound used include BaCO3, BaO, BaCl2, Ba(NO3)2 and Ba[OCH(CH3)2]2. Examples of the Mn compound used include MnF2, MnCl2, MnO and Mn(NO3)2.XH2O wherein X is an integer of 4 through 6. Examples of the Al compound used include Al2O3 and Al(OH)3. Examples of the B compound used include B2O3 and H3BO3.
Next, the mixture of the Ba, Mn, Al and B compounds is sufficiently stirred and then primarily fired at 1000 to 1500xc2x0 C. in the presence of air, preferably at 1300 to 1350xc2x0 C. for 0.5 to 5 hours.
Thereafter, the resultant material is secondarily fired at 1000 to 1500xc2x0 C. under a reducing gas atmosphere, preferably at 1300 to 1350xc2x0 C. for 0.5 to 3 hours. The reason of conducting secondary firing under a reducing gas atmosphere is to eliminate an oxidative atmosphere caused by conducting the primary firing in the presence of air and to reduce partially oxidized materials. The reducing gas is not specifically restricted but a mixed gas of nitrogen and hydrogen in the mixture volume ratio of 95 to 5 may be used.
During firing, if the temperature of the primary and secondary firing steps deviates from the above-described range, the luminance of the finally obtained phosphor is undesirably poor.
The phosphor obtained after the secondary firing is washed with 1 to 20% aqueous hydrochloric solution, washed with water, and then dried to obtain a green-emitting phosphor represented by the formula (1). Here, the reason of washing the obtained phosphor with an aqueous hydrochloric solution is to remove unreacted materials or defects remaining on the surface of the phosphor. The drying temperature performed after washing with water is preferably 50 to 120xc2x0 C. Here, if the drying temperature is lower than 50xc2x0 C., too much time is required for drying. If the drying temperature is higher than 120xc2x0 C., aggregation of phosphor particles undesirably occurs.
The green-emitting phosphor obtained according to the above-described method has excellent color purity and luminance characteristics. Also, the obtained green-emitting phosphor increases the white color temperature of a panel to 9000 K or higher. Thus, the picture quality of a PDP can be improved by applying these characteristics to the PDP.
Hereinbelow, the present invention is described more concretely with reference to specific examples intended to illustrate the invention without limiting the scope thereof.